Delivery of nucleic acids to the cell nucleus not only can support basic investigations into intracellular biological mechanisms1-3, but also may pave the way for treating diseases by regulating the expression of target genes4-5. Intranuclear delivery is challenging due to the need to penetrate through both the cell membrane and nuclear membrane4-5. Despite the plethora of methods available for crossing the cell membrane, many of them do not guarantee specific delivery to the nucleus ensuing cellular entry (e.g., electroporation6, transfection agent7-8, nanoparticles9). Viral vectors are effective for overcoming the nuclear membrane, yet suffer from concerns over cytotoxicity and immune response10-11. Non-viral methods usually entail laborious handling (e.g., microinjection12), extensive fabrication (e.g., microneedles13), or costly conjugation of targeting biomolecules (e.g., nuclear localization peptides14-15, aptamers16).
Investigations into intranuclear delivery of polynucleotides by applying external pressure to cells were scarce and include gene gun17 and microneedles18. Gene gun and microneedles required the application of pressure on the order of 104-105 Pa, but do not guarantee specific delivery to the nucleus. Another example of specific intranuclear delivery of oligonucleotides entailed the use of fluid pressure: By infusing a saphenous vein with a fluid that contains micromolar concentrations of DNA at 100 mmHg (i.e., 13,300 Pa) for 10 min, the authors observed intranuclear delivery to 60% of the cells in the myocardium ex vivo19. Despite the high transfection efficiency, this method involves cannulation and may distort cell morphology. Indeed, applying pressure on the order of 102-103 Pa to cells may perturb normal cellular functions. Applying a compressive stress of 100 Pa for 10 h can damage 35% of the myoblasts20. Exerting a compressive stress of 5.8 mmHg (i.e., 770 Pa) on cancer cells for 16 h will drive their phenotype to become invasive in the tumor microenvironment21.